It is normal for different people to have different understandings of what Cloud Computing is. I will detail the basics below:
According to the The National Institute of Technology :
A model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.
This cloud model is composed of five essential characteristics, three service models, and four deployment models
The Five Essential Characteristics
- On-Demand Self-Service. Resources can be unilaterally allocated with or without automation.
- Broad Network Access. Capabilities and/or services are available over the network and accessible via standard mechanisms: Mobile, Workstation, Servers, etc.
- Resource Pooling. Many customers use the same resources, this is known as multitenancy.
- Rapid Elasticity. New Capabilities can be provisioned automatically, ex: A new Virtual machine in a Scaleset
- Measure Price. You pay what you consume. Every resource will have a different cost metric, ex: Storage, Virtual Machines, Databases, etc.
The Three Service Models
Software as a Service (SaaS): The provider runs the software and the customer can adjust it to its needs. The customer has no access to the underlying infrastructure. Ex: Office 365, SalesForce.
Platform as a Service (PaaS): The consumer builds and/or deploy applications to the provider’s infrastructure. The consumer doesn’t manage the infrastructure but may have access to some parts of it.
Infrastructure as a Service (IaaS): The most common of all. The customer has full control of storage, compute power, networking, operating system, etc and call install any software.
The Four Deployment Models
Public Cloud. Most customers go with Public Cloud vendors, ex: Azure or AWS while implementing their security and operational controls.
Private Cloud. The infrastructure is installed for the exclusive use of a specific customer. ex: Azure Stack
Hybrid Cloud: The combination of multiple Cloud Providers, ex: Google Cloud for Object Storage and Azure for IaaS workloads.
Community Cloud: The cloud infrastructure is provisioned for exclusive use by a specific community of consumers, ex: AWS and Azure Goverment Cloud.
The NIST Definition of Cloud Computing